package/mender-grubenv: bump version to f39c2c7ec7c9c24aae0108a9b04a0e6e61a3e96b

package/mender-grubenv: bump version to f39c2c7ec7c9c24aae0108a9b04a0e6e61a3e96b

According to the developers, mender-grubenv is no longer tagging releases for
the mender-grubenv project. However, they asked me if I could submit a patch
upstream to update the package to the latest commit, including quality of life
improvements since the last official 1.3.0 release.

Notable improvements are:
  - Support for separate A/B kernel partitions.
  - Use regexp to dynamically set mender_grub_storage_device
  - Add "rootwait" as a default rootfs argument

Other changes:
  - Update license hashes due to a copyright year bump.

Signed-off-by: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>